This disclosure relates to lubricants in air-conditioning and refrigeration (AC/R) systems, and in particular to an additive composition for conditioning lubricants pre-existing in such AC/R systems.
Hydrofluorocarbon (HFC) refrigerants are now often used to replace legacy hydrochlorocarbon (HCC) and hydrochlorofluorocarbon (HCFC) refrigerants in existing AC/R systems. However, such a change over often requires additional component upgrades or results in reduced system performance.
In an ideal situation, a drop-in refrigerant would replace an HCFC refrigerant such as R-22 directly with no change to existing components or equipment or the operating efficiencies of the AC/R system. Current replacement refrigerants include retrofit replacement refrigerants which require a change out of one or more AC/R system components such as elastomeric seals, filter driers, metering devices and oil. For example, HFC R-410A, which is a retrofit replacement refrigerant for R22, requires a condenser unit change. Refrigeration systems operating with R-410A operate at higher pressures and the compressor requires a thicker shell wall than when R-22 is used. A metering device change is also required and a change in the evaporator coil is also recommended when changing to R-410A.
Current replacement refrigerants also include refrigerants intended for drop-in such as the HFC mixture R-421A, which can replace HCFC R-22 without any retrofits but can result in lower efficiency depending on factors such as high ambient operating conditions and systems overall performance due to piping arrangements, or heat exchange of the condenser and evaporator coils as it pertains to refrigerant flow and air exchange.
Other drop-in refrigerants such as R-417a and R-422a contain a small amount of hydrocarbon (butane or isobutene) to allow continued use of existing mineral or alkylbenzene oils in the system. The hydrocarbon in the refrigerant is intended to improve oil return back to the compressor by reducing oil viscosity. Using only a low concentration of hydrocarbon ensures the refrigerant remains non-flammable. In fact, the small amount of hydrocarbon actually contributes to lower oil return, resulting in oil logging and reduced heat transfer. It is well established that retrofit refrigerants result in reduced system capacity, increased energy usage, and failure to meet load demands at higher ambient temperatures.
When changing to a replacement refrigerant, an important factor to consider is the choice of compressor lubricant oil. HCFC refrigerants such as R-22 use compressor oils based on the use of hydrocarbon bases, namely mineral oil or alkyl benzenes. However, these lubricants are not sufficiently miscible with HFC refrigerants. Miscibility between refrigerant and lubricant is required to return entrained lubricant from system lines back to the compressor to ensure adequate ongoing lubrication. The change to HFC refrigerants therefore requires also a change-out of lubricant from these immiscible lubricants to lubricants such as the polyol esters which are miscible with an HFC refrigerant such as R-134a.
As a result of the above considerations, typical refrigerant change procedures involve one or more additional steps of replacing the existing condenser and evaporator, draining lubricant and then flushing the existing refrigeration system line sets with solvent to remove any residual mineral or alkyl benzene oils. Solvent flushes require high pressure nitrogen purges as a final further step to remove the remaining solvent flush from the refrigeration system lines.